Various important technological applications employ thin film resistors. These thin film resistors may be integrated in individual integrated semiconductor devices or they can be located in complex hybrid circuits or integrated circuits. Thin film resistors may be arranged as resistive ladder networks in analog-to-digital converters, or as current limiting and/or load resistors in various different circuits such as amplifiers, filters, current or voltage buffering or biasing stages etc.
Thin film resistors may comprise various different materials, as for example tantalum nitride (TaN), silicon, chromium (SiCr), or nickel chromium (NiCr). These resistor materials are generally evaporated or sputtered onto a substrate wafer at a metal interconnect level and subsequently patterned and etched. In order to use the thin film resistors, they have to be electrically connected. The parameters and performance of the thin film resistors is then related to the condition and to the quality of the resistor surface and the electrical connection. However, within the established manufacturing processes for integrated semiconductor devices, it is challenging to contact thin film resistors without impairing or destroying important parameters or even the thin film transistors themselves.
U.S. Pat. No. 6,921,962 B1 discloses a semiconductor device and a method for manufacturing a semiconductor device with a thin film resistor. As shown in FIG. 1 of the reference, conductively filled VIAs 95 extend from the upper metal interconnect layer 100 to the thin film resistors 60 and a lower metal interconnect layer 40. The VIAs are formed simultaneously, with no processing steps being added to contact resistors 60. VIAs 95 preferably contact optional portions of hard mask 70 that remain over the ends of resistor material 60. However, VIAs 95 may contact resistor material 60 and/or hard mask 70. Optional hard mask portions 70 can protect resistor material 60 during the VIA etch. Hard mask portions 70 comprise a conductive material such as titanium-tungsten (TiW), titanium-nitride (TiN) or molybdenum (Mo). Resistor material 60 can comprise materials such as tantalum-nitride (TaN), silicon-chromium (SiCr), or nickel chromium (NiCr).
U.S. Pat. No. 7,112,286 B2 discloses a thin film resistor structure which includes an electrical interface layer or head layer that is a combination of a titanium (Ti) layer and a titanium nitride (TiN) layer. The combination of the Ti layer and the TiN layer mitigates resistance associated with the electrical interface. Additionally, the employment of the Ti layer provides a more reproducible resistivity value associated with the electrical interface layer. Furthermore, the Ti layer acts as a glue layer to facilitate adhesion of the TiN to the thin film resistor material.
In order to connect lower level interconnect layers of, for example aluminum, the interconnect layers traditionally were covered by a titanium nitride layer (TiN). A hole for a VIA is then etched by a strong pre-sputter etch step in order to remove the TiN layer and reach the aluminum layer below. Subsequently, the opening for the VIA is covered with a liner of titanium (Ti) and then with a liner of TiN. Finally, the remaining space within the opening is filled with tungsten in order to electrically connect the lower level interconnect layer with a higher level. This strong pre-sputter etch for removing the TiN layer on top of the aluminum is not compatible with VIA etching for connecting a thin film resistor layer as the thin film resistor layer may easily be destroyed.